This small intestinal digestive oligosaccharidases are being isolated and characterized so that it will be possible to better understand the mechanism of carbohydrate assimilation. Emphasis is being placed on the hybrid brush border enzyme sucrase-isomaltase which appears to be a brush border membrane protein. The enzyme has been purified to homogeneity and a monospecific antibody is being used to probe the location of synthesis within the intestinal cell and to allow study of the synthesis and degradation under conditions of various diets including regular, 70 percent carbohydrate, carbohydrate-free, and low protein. The localization of this enzyme within the membrane is being probed by use of covalent radioactive molecules from the luminal surface as well as from isolated brush border membranes and protein-solubilized brush border membranes. It is hoped that it will be possible to define the mechanisms whereby the enzyme is assembled within the depths of the cell and subsequently transferred into the brush border membrane to play its functional role.